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PDF image extraction in Kotlin

Sample Kotlin code for using PDFTron SDK to extract images from PDF files, along with their positioning information and DPI. Instead of converting PDF images to a Bitmap, you can also extract uncompressed/compressed image data directly using element.GetImageData() (described in the PDF Data Extraction code sample). Learn more about our PDF Parsing & Content Extraction Library.

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//---------------------------------------------------------------------------------------
// Copyright (c) 2001-2019 by PDFTron Systems Inc. All Rights Reserved.
// Consult legal.txt regarding legal and license information.
//---------------------------------------------------------------------------------------

package com.pdftron.android.pdfnetsdksamples.samples

import com.pdftron.android.pdfnetsdksamples.OutputListener
import com.pdftron.android.pdfnetsdksamples.PDFNetSample
import com.pdftron.android.pdfnetsdksamples.R
import com.pdftron.android.pdfnetsdksamples.util.Utils
import com.pdftron.common.PDFNetException
import com.pdftron.pdf.Element
import com.pdftron.pdf.ElementReader
import com.pdftron.pdf.Image
import com.pdftron.pdf.PDFDoc
import java.util.*

///-----------------------------------------------------------------------------------
/// This sample illustrates one approach to PDF image extraction
/// using PDFNet.
///
/// Note: Besides direct image export, you can also convert PDF images
/// to Java image, or extract uncompressed/compressed image data directly
/// using element.GetImageData() (e.g. as illustrated in ElementReaderAdv
/// sample project).
///-----------------------------------------------------------------------------------

class ImageExtractTest : PDFNetSample() {
    init {
        setTitle(R.string.sample_imageextract_title)
        setDescription(R.string.sample_imageextract_description)

        // The standard library does not support exporting to
        // PNG/TIFF formats, thus trying to export the PDF to
        // PNG or TIFF will fail. Please, comment out this call
        // if using the full library.
        // DisableRun();
    }

    override fun run(outputListener: OutputListener?) {
        super.run(outputListener)
        mOutputListener = outputListener
        mFileList.clear()
        printHeader(outputListener!!)
        // Initialize PDFNet

        // Example 1:
        // Extract images by traversing the display list for
        // every page. With this approach it is possible to obtain
        // image positioning information and DPI.
        try {
            val doc = PDFDoc(Utils.getAssetTempFile(PDFNetSample.INPUT_PATH + "newsletter.pdf")!!.absolutePath)
            doc.initSecurityHandler()

            val reader = ElementReader()
            //  Read every page
            val itr = doc.pageIterator
            while (itr.hasNext()) {
                reader.begin(itr.next())
                ImageExtract(reader)
                reader.end()
            }

            doc.close()
            mOutputListener!!.println("Done...")
        } catch (e: Exception) {
            mOutputListener!!.printError(e.stackTrace)
        }

        mOutputListener!!.println("----------------------------------------------------------------")

        // Example 2:
        // Extract images by scanning the low-level document.
        try {
            val doc = PDFDoc(Utils.getAssetTempFile(PDFNetSample.INPUT_PATH + "newsletter.pdf")!!.absolutePath)

            doc.initSecurityHandler()
            image_counter = 0

            val cos_doc = doc.sdfDoc
            val num_objs = cos_doc.xRefSize()
            for (i in 1 until num_objs) {
                val obj = cos_doc.getObj(i)
                if (obj != null && !obj.isFree && obj.isStream) {
                    // Process only images
                    var itr = obj.find("Type")
                    if (!itr.hasNext() || itr.value().name != "XObject")
                        continue

                    itr = obj.find("Subtype")
                    if (!itr.hasNext() || itr.value().name != "Image")
                        continue

                    val image = Image(obj)

                    mOutputListener!!.println("\n-. Image: " + ++image_counter)
                    mOutputListener!!.println("\n    Width: " + image.imageWidth)
                    mOutputListener!!.println("\n    Height: " + image.imageHeight)
                    mOutputListener!!.println("\n    BPC: " + image.bitsPerComponent)

                    val fname = "image_extract2_$image_counter"
                    val path = Utils.createExternalFile(fname, mFileList).absolutePath
                    image.export(path)

                    //String path= Utils.createExternalFile(fname + ".tif", mFileList).getAbsolutePath();
                    //image.exportAsTiff(path);

                    //String path = Utils.createExternalFile(fname + ".png", mFileList).getAbsolutePath();
                    //image.exportAsPng(path);
                }
            }

            doc.close()
        } catch (e: Exception) {
            mOutputListener!!.printError(e.stackTrace)
        }

        for (file in mFileList) {
            addToFileList(file)
        }
        printFooter(outputListener)
    }

    companion object {

        private var mOutputListener: OutputListener? = null

        private val mFileList = ArrayList<String>()

        // Relative paths to folders containing test files.

        internal var image_counter = 0

        @Throws(PDFNetException::class)
        internal fun ImageExtract(reader: ElementReader) {
            var element: Element?
            while (true) {
                element = reader.next()
                if (element == null) {
                    break
                }
                when (element.type) {
                    Element.e_image, Element.e_inline_image -> {
                        mOutputListener!!.println("\n--> Image: " + ++image_counter)
                        mOutputListener!!.println("\n    Width: " + element.imageWidth)
                        mOutputListener!!.println("\n    Height: " + element.imageHeight)
                        mOutputListener!!.println("\n    BPC: " + element.bitsPerComponent)

                        val ctm = element.ctm
                        val x2 = 1.0
                        val y2 = 1.0
                        ctm.multPoint(x2, y2)
                        mOutputListener!!.println("\n    Coords: x1=" + ctm.h +
                                ", y1=" + ctm.v + ", x2=" + x2 + ", y2=" + y2)

                        if (element.type == Element.e_image) {
                            val image = Image(element.xObject)

                            val fname = "image_extract1_$image_counter"

                            val path = Utils.createExternalFile(fname, mFileList).absolutePath
                            image.export(path)

                            val path2 = Utils.createExternalFile("$fname.tif", mFileList).absolutePath
                            image.exportAsTiff(path2)

                            val path3 = Utils.createExternalFile("$fname.png", mFileList).absolutePath
                            image.exportAsPng(path3)
                        }
                    }
                    Element.e_form        // Process form XObjects
                    -> {
                        reader.formBegin()
                        ImageExtract(reader)
                        reader.end()
                    }
                }
            }
        }
    }

}
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